We propose to establish cellular biomarkers in human neurons differentiated from induced pluripotent stem cells (iPSC) of Alzheimer's disease (AD) patient origin to predict specific drug responses. These human cell lines will be used as an ex vivo cellular model to characterize key proteins driving AD pathogenesis, amyloid protein (A) and Tau, and to correlate to postmortem brain pathology from the same donor. We will also collect postmortem brain and CSF samples from the same donor. We will quantify A monomers and oligomers, pTau and Tau levels and validate intrinsic properties of these biomarkers in cells and brain tissues. We will test the hypotheses that neurons having higher A or pTau proteins respond to therapeutic agents differently. By testing this hypothesis, we will address a critical question in AD therapeutic development, whether characteristic A/Tau biomarkers can be used to predict therapeutic efficacy in sporadic AD (SAD) patients. Currently, biomarkers consisting of a combination of brain amyloid imaging and cerebrospinal fluid (CSF) A and pTau/Tau proteins have been developed and are used in patient selection for clinical trials. There is no in vitro method of testing AD biomarkers to predict individual's brain pathology and CSF profile without performing brain amyloid imaging and CSF collection. We are uniquely positioned to carry out these studies. We have almost two-decades of experience in cellular modeling for AD research and a well-characterized patient population contributing blood cells and postmortem tissue for ex vivo modeling and in vivo confirmation. Work in my laboratory has used the mammalian cell culture model to study the functional role of presenilin in amyloid precursor protein (APP) processing and A generation. Using extensive biochemical assays and highly sensitive ELISA, we have quantified various isoforms of A and Tau proteins in cultured cells, animals, and human tissues. In bringing this expertise to bear on human iPSC, we will directly assess the A and Tau protein signatures in AD-derived human neurons and use this signature to predict the responses to therapeutics. Our Institutional Review Board (IRB) application has been approved, and 29 subjects have been consented for participation. All participants have agreed, by proxy, to brain autopsy to confirm the diagnosis of AD. We will derive iPSC from patients living at an inpatient AD hospice unit, where life expectancy is 6 months or less. Blood cells will be used for iPSC preparation. Ventricular CSF and postmortem brain tissues will be collected from the same individuals who have donated blood cells for iPSC preparation. Clinical diagnosis will be confirmed by detailed neuropathological evaluation and characterization. By creating iPSC originating from AD patients, this work will generate iPSC-derived human neuronal cells that carry different signatures of A/Tau proteins. To avoid the variation introduced in the course of iPSC conversion and differentiation, we will compare the changes of A/Tau in same neuronal cell lines with or without pharmacologic treatment and predict responses to different therapeutic agents. Specifically, we will achieve the following aims. Aim 1. To determine whether the A/Tau protein signature in iPSC-derived human neurons is consistent with that in postmortem brain tissue from the same donor. Established methods will be applied to convert blood cells to iPSC, followed by differentiation into neuronal cells. We will quantify the A monomer and oligomer proteins, total and pTau proteins. We will determine whether levels of A and Tau/pTau in cultured neurons are inherently reflected in postmortem CSF and brain tissue from the original cell donors, validating cellular biomarkers for therapeutic tests. Aim 2. o determine whether levels of A and pTau predict cellular responses to secretase or kinase inhibitors. Human neurons with different levels of A/Tau will be treated with a -secretase inhibitor, and the effect on A42 and A oligomers will be quantified. GSK3 inhibitor will be used to reduce Tau phosphorylation. We will determine whether high levels of A or pTau in cultured neurons predict better responses to secretase and kinase inhibitors, respectively.